Yes, winter is back, and while we can all look forward to the excesses of the festive season, there's one element of the colder months that nobody enjoys - getting ill.

As well as sniffles, cold and flu there's also one dreaded bug that rears its ugly head every year. Known as norovirus, the vomiting bug is high infectious and can be spread by coming into close contact with someone who has it, touching contaminated surfaces or objects and eating contaminated food.

Here, Dr Roger Henderson explains what norovirus is, how it affects the body and what you can do to avoid getting it.

What is norovirus?

More unpleasantly known as the 'winter vomiting bug', this highly contagious viral infection is the silent fun-killer of every office, lurking in keyboards and on taps, ready to take down unsuspecting workers right before the Christmas party.

In the UK, norovirus is the most common stomach bug, with between 600,000 and one million people contracting it each year, explains GP Dr Roger Henderson.

"The virus is incredibly contagious and can be passed on through contact with an infected person, or contact with contaminated surfaces or objects. Faecal matter can also carry the virus, meaning it can be found on toilet seats and handles," he explains.

"You can also get norovirus from contaminated food and water, especially foods such as oysters, mussels, clams, cockles and scallops."

As well as the obvious breeding ground of the office, other germ hotspots include public transport and schools.

It will bring you down fast

The virus particles are extremely fast-acting, and are usually ingested through either your mouth or nose. It has a very short incubation period, and once you've come into contact with the virus, it only takes 12-48 hours for symptoms to kick in.

It hits the stomach first, but it's only when norovirus arrives at the small intestine that it really begins to multiply (this is generally when you start to feel the first twinges of nausea). Much like a parasite, the virus is not able to operate as a single agent - it needs living cells to feed from. Once it's gained control, it's able to spread like wildfire by attaching itself to healthy cells in the lining the intestine.

During this early incubation period, the infected cells explode, producing replicas of the virus and releasing more infected particles into the bloodstream.

For 48 hours you'll feel very unwell. You may experience sudden projectile vomiting and watery diarrhoea as your body attempts to fight the infection. These are your body's natural trigger-responses, as your immune system toils to flush the particles out of your body. (The irony is, the virus affects the small intestine, not the stomach, which means vomiting and diarrhoea do very little to help.)

Dr Henderson notes that you may experience stomach cramps, abdominal pain, fatigue and a mild fever while you're contagious.

The good news is, norovirus tends to leave as quickly as it arrives, usually lasting one to two days. People generally find they continue to feel weak for a few days afterwards, as the immune systems works overtime to battle against the infection, gradually locating the infected cells and deactivating them.

"There is no specific treatment for the virus but to let the illness run its course," says Dr Henderson. "While the symptoms are not pleasant, most people make a full recovery within a few days. Both vomiting and diarrhoea cause loss of water from the body, so you need to drink plenty of liquids to replace lost fluids. Antidiarrheal medicines such as loperamide can ease symptoms, while paracetamol helps aches and pains."

There are ways to keep the virus at bay

Your best course of action is to practice good hygiene. Washing your hands after using the toilet should involve a good scrub with anti-bacterial soap, not just a quick splash of water before you run out of the bathroom.